A universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from a global system for mobile communications system (GSM), which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access technologies.
A related art UMTS network structure 1 is illustrated in FIG. 1. As shown, a mobile terminal, or user equipment (UE) 2 is connected to a core network (CN) 4 through a UMTS terrestrial radio access network (UTRAN) 6. The UTRAN 6 configures, maintains and manages a radio access bearer for communications between the UE 2 and the core network 4 to meet end-to-end quality of service requirements.
The UTRAN 6 includes a plurality of radio network subsystems (RNS) 8, each of which comprises one radio network controller (RNC) 10 for a plurality base stations, or Node Bs 12. The RNC 10 connected to a given base station 12 is the controlling RNC for allocating and managing the common resources provided for any number of UEs 2 operating in one cell. One or more cells exist in one Node B. The controlling RNC 10 controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B 12 may receive an uplink signal from a UE 2 and may transmit a downlink signals to the UE 2. Each Node B 12 serves as an access point enabling a UE 2 to connect to the UTRAN 6, while an RNC 10 serves as an access point for connecting the corresponding Node Bs to the core network 4.
Among the radio network subsystems 8 of the UTRAN 6, the serving RNC 10 is the RNC managing dedicated radio resources for the provision of services to a specific UE 2 and is the access point to the core network 4 for data transfer to the specific UE. All other RNCs 10 connected to the UE 2 are drift RNCs, such that there is only one serving RNC connecting the UE to the core network 4 via the UTRAN 6. The drift RNCs 10 facilitate the routing of user data and allocate codes as common resources.
The interface between the UE 2 and the UTRAN 6 is realized through a radio interface protocol established in accordance with radio access network specifications describing a physical layer (L1), a data link layer (L2) and a network layer (L3) described in, for example, 3GPP specifications. These layers are based on the lower three layers of an open system interconnection (OSI) model that is a well-known in communications systems.
A related art architecture of the radio interface protocol is illustrated in FIG. 2. As shown, the radio interface protocol is divided horizontally into a physical layer, a data link layer, and a network layer, and is divided vertically into a user plane for carrying data traffic such as voice signals and Internet protocol packet transmissions and a control plane for carrying control information for the maintenance and management of the interface.
The physical layer (PHY) provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. Data travels between the MAC layer and the physical layer via a transport channel. Also, data transmission is performed through a physical channel between different physical layers, namely, between physical layers of a sending side (transmitter) and a receiving side (receiver).
The MAC layer of the second layer (L2) provides information transfer service to a higher layer and is linked via a logical channel to a radio link control (RLC) layer. The RLC layer of the second layer (L2) supports the transmission of reliable data and can perform segmentation and concatenation functions for RLC service data units (SDU) received from an upper layer.
A radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane and controls transport channels and physical channels with respect to the establishment, re-establishment, and release of radio bearers. A radio bearer (RB) is a service provided by a lower layer, such as the RLC layer or the MAC layer, for transferring data between the UE 2 and the UTRAN 6.
The establishment of an RB determines regulating characteristics of the protocol layer and channel needed to provide a specific service, thereby establishing the parameters and operational methods of the service. When a connection is established to allow transmission between an RRC layer of a specific UE 2 and an RRC layer of the UTRAN 6, the UE 2 is said to be in the RRC-connected state. Without such connection, the UE 2 is in an idle state.
Hereafter, a Multimedia Broadcast/Multicast Service (MBMS or “MBMS service”) will be described. MBMS refers to a method of providing streaming or background services to a plurality of UEs 2 using a downlink-dedicated MBMS radio bearer that utilizes at least one of point-to-multipoint and point-to-point radio bearer. One MBMS service includes one or more sessions and MBMS data is transmitted to the plurality of terminals through the MBMS radio bearer only while the session is ongoing.
As the name implies, an MBMS may be carried out in a broadcast mode or a multicast mode. The broadcast mode is for transmitting multimedia data to all UEs 2 within a broadcast area, for example the domain where the broadcast is available. The multicast mode is for transmitting multimedia data to a specific UE 2 group within a multicast area, for example the domain where the multicast service is available.
The UTRAN 6 provides the MBMS service to the UEs 2 using the RB. RBs used by the UTRAN 6 can be classified as a point-to-point RB or a point-to-multipoint RB. The point-to-point RB is a bi-directional RB, including a logical channel DTCH (Dedicated Traffic Channel), a transport channel DCH (Dedicated Channel) and a physical channel DPCH (Dedicated Physical Channel) or SCCPCH (Secondary Common Control Physical Channel).
The point-to-multipoint RB is a uni-directional downlink RB, including a logical channel MTCH (MBMS Traffic Channel), a transport channel FACH (Forward Access Channel), and the physical channel SCCPCH, as shown in FIG. 3. The logical channel MTCH is configured for each MBMS service provided to one cell and used to transmit user plane data of a specific MBMS service to the UEs 2.
The UTRAN 6 providing the MBMS service transmits MBMS-related control information to the plurality of terminals (UEs 2) through an MCCH (MBMS Control Channel). Herein, the logical channel MCCH is the point-to-multipoint downlink channel and is mapped to the FACH, which is mapped to the SCCPCH. The MBMS-related control information includes a session start for indicating the start of an MBMS service, a session stop for indicating the end of the MBMS service, an RB type indicator for indicating whether the MBMS service is provided via a point-to-point RB or a point-to-multipoint RB, RB information for providing point-to-multipoint RB information such as the MTCH if the RB is a point-to-multipoint RB, counting information for measuring the number of terminals desiring to receive the MBMS service, and re-counting information for re-counting the number of terminals desiring the MBMS service while the MBMS service is being provided.
FIG. 3 illustrates channel mapping for an MBMS of a UE side. The MBMS-related control information may be included in an independent message and transmitted, or can be entirely included in one MBMS control message. To transmit various control information related to the MBMS service, the logical channel MCCH is used. Channel mapping of the MCCH is similar to that of the MTCH. Namely, the MCCH is a point-to-multipoint downlink channel and is mapped to the transport channel FACH, which is mapped to the physical channel SCCPCH. For reference, only one MTCH is provided for one service, while only one MCCH is provided for one cell.
The terminal (UE) 2 wishing to receive an MBMS service, must first receive MBMS control information through the MCCH. However, because the terminal 2 can receive only one SCCPCH for the MBMS, and the MCCH is transmitted through a different SCCPCH irrelative to the MTCH, the terminal cannot receive the MCCH if the terminal has already received one or more MBMS services.
FIG. 4 illustrates a related art method for transmitting MCCH information. The MCCH information is periodically transmitted according to a modification period and a repetition period. Furthermore, the MCCH information is divided into critical information and non-critical information. The non-critical information may be easily modified during each modification period and repetition period to be transmitted. However, the critical information may be modified only during each modification period to be transmitted. As such, the critical information may be repeatedly transmitted once per repetition period; however, modified critical information may be transmitted only at a beginning point of the modification period.
A UE desiring to receive a specific MBMS service using a point-to-multipoint RB receives the MCCH information including RB information through an MCCH channel. The UE then establishes the point-to-multipoint RB using the MCCH information. Once the point-to-multipoint RB is established, the UE continues to receive a physical channel SCCPCH, to which an MTCH is mapped, to obtain specific MBMS service data transmitted through the MTCH.
FIG. 5 is an example of a transmission of discontinuous MBMS data, scheduling information and a Secondary Notification Indicator (SNI) through a physical channel SCCPCH. The UTRAN can discontinuously transmit MBMS data through an MTCH. At the same time, the UTRAN can periodically transmit scheduling information to the UE through an SCCPCH to which the MTCH is mapped. Here, the scheduling information notifies the UE of a transmission interval of the MBMS service transmitted during one scheduling period. Previously, the UTRAN notified the UE of a transmission period of the scheduling information, namely, the scheduling period, to allow the UE to receive the scheduling information. Therefore, once the UE has obtained the scheduling period from the UTRAN, the UE then receives the scheduling information according to the obtained scheduling period. The UE also discontinuously receives the SCCPCH to which the MTCH is mapped by using the received scheduling information.
Still referring to FIG. 5, while the MTCH for a specific MBMS service is established, the UTRAN can transmit a secondary notification indicator (SNI) to the UE through the SCCPCH to which the MTCH is mapped. When MCCH information for a certain MBMS service is transmitted through the MCCH, the SNI notifies the MCCH information transmission to the UE receiving a corresponding MTCH. In other words, when the MCCH information to be transmitted through the MCCH exists, the UTRAN transmits the SNI to the UE through the SCCPCH to which the MTCH is mapped. Therefore, the UE first receives the SNI through the SCCPCH and then receives the MCCH according to an indication of the SNI. The UE then receives the MCCH information through the MCCH. The SNI can be transmitted or received through the MTCH or through another logical channel mapped to the SCCPCH together with the MTCH.
However, in the related art, the UE cannot recognize when the SNI is to be transmitted. For instance, as shown in FIG. 4, when the UE discontinuously receives the SCCPCH to which the MTCH is mapped according to the scheduling information, only a transmission interval of the MBMS data is notified by the scheduling information. As a result, the UE receives the SCCPCH only during an interval that the MBMS service is transmitted.
Therefore, the UE discontinuously receiving the SCCPCH to which the MTCH is mapped may not receive the SNI. When the SNI is not received, the corresponding UE may not receive a notification message, which the UTRAN transmits through the MCCH.